1. Field of the Invention
The present invention relates to lasers and more particularly to an improved optically-pumped solid state laser.
2. Description of the Prior Art
Many solid state lasers are directly pumped by flashlamps located in proximity to the lasing material. Since flashlamps radiate power across a broad spectral band, an attempt is usually made to match the emission and absorption wavelengths to maximize the overall laser excitation efficiency. Unfortunately, the number of available lamp and laser media that meet this criteria is so small that most lasers are severely restricted in their overall efficiency by pumping spectral mismatches.
Prior attempts to solve spectral mismatches have involved the use of fluorescent converters, which are selected so that the converter:
(1) transmits most or all of the flashlamp radiation which is directly within the absorption band of the laser host; and
(2) absorbs a substantial portion of the flashlamp radiation which is outside the absorption band of the laser host. By molecular or atomic processes, fluorescent converters re-emit radiation (i.e., fluoresce) efficiently in a wavelength band which is within the absorption band of the laser host.
The only known example of the successful application of fluorescent conversion to date has been with liquid solutions of dyes within which the solid state laser medium is immersed. The significant benefits of this technique include a substantial enhancement of efficiency. For example, a flashlamp pumped neodymium yttrium aluminum garnet (Nd:YAG) laser and a Rhodamine 6G dye solution within its coolant experienced an increase in efficiency of approximately 30%. For a Ti:sapphire laser using a Coumarin dye solution, flashlamp pumped laser action was achieved at approximately 0.5% efficiency, (as compared to no lasing without the fluorescent converter). One disadvantage of this technique is short dye lifetime due to photochemical disassociation of the dye molecules with subsequent loss of absorption/fluorescence efficiency. Additionally, the difference between the refractive indices of the fluorescent material (n=1.3) and of the lasing medium (n=1.8) causes substantial Fresnel reflections at the surface, causing a loss of the isotropic fluorescent radiation due to re-absorption by the flashlamp.
This invention is directed to a flashlamp pumped solid-state laser which avoids these disadvantages.